The present invention generally relates to aircraft insulation systems employed to reduce the loss of heat from the aircraft cabin to the surrounding ambient atmosphere. More particularly, the present invention relates to a new hot bleed air distribution and insulation system which completely eliminates the need for conventional insulation blankets, thereby significantly reducing the aircraft manufacturer's material and production costs as well as the operator's corrosion repair costs.
Insulation blankets are currently employed on passenger aircraft to provide acoustic attenuation of wind noise and, more importantly, to reduce the loss of heat from the interior of an aircraft passenger cabin. A conventional insulation blanket system disclosed in U.S. Pat. No. 2,427,698 requires electrical heaters to heat and blowers to circulate heated air throughout the cabin.
At cruising altitudes achieved by today's jet aircraft, ambient temperature often drops as low as -40.degree. C., causing water vapor inside the aircraft cabin to condense onto cold metallic surfaces and become absorbed by conventional insulation blankets located in passageways extending between the passenger cabin wall panels and the outside skin of the aircraft fuselage. As a result, the weight of the insulation material can often increase the total weight of the insulation blankets by a factor of three over a three year period of time. Because wet insulation blankets have a higher thermal conductivity than dry blankets, the heat transfer rate increases, reducing the insulating effect of the blankets.
Wet insulation blankets create a number of expensive problems in the aircraft industry. The water absorbed by the insulation blankets causes corrosion of the aircraft structure. Repairing the resulting corrosion damage to the aircraft structure is very costly and may require the aircraft to be pulled from normal operation during repair. Many cases of water actually dripping into the cabin (known as "Rain in the Plane") are known to have occurred.
Insulation blankets employed in a conventional twinjet aircraft have been documented to retain an average maximum weight of 1,500 lb. and an average minimum weight of 330 lb. of water. Trijet aircraft have been documented to retain an average maximum weight of 2400 lb. and an average minimum weight of 660 lb. of water. It has been estimated that the water carried by the insulation blankets requires extra fuel costing about $14,000.00 per year per twinjet and that the water is responsible for up to five percent of the overall corrosion repair costs. While these changes in weight and resulting fuel increases may not arise with every aircraft, they are believed to be typical of the problems associated with employing insulation blankets.
In order to combat the adverse effects of water absorption by convention al insulation blankets, U.S. Pat. No. 3,740,905 suggests that insulation blankets be arranged to allow condensing moisture to drain and be collected in a central collection point. The collected water is then used to introduce humidity into the passenger compartment. As will become clear, the present invention significantly reduces the need for insulation blankets as well as a separate humidifier system.
Recognizing the need to maintain dry insulation blankets, U.S. Pat. No. 5,577,688 suggests a process and structure wherein moisture condensed within a bag of insulation material is allowed to pool under gravity, with air flowing through the enclosed space containing the bags removing the condensed liquid. While the '688 patent attempts to solve the problem by equalizing the pressure within individual insulation blankets using a source of dry air as opposed to humid cabin air, once again the corrosion and weight problems associated with insulation blankets are, at best, only somewhat reduced, and not eliminated.
Based on the above and foregoing, it can be appreciated that there presently exists a need in the art for a system and method capable of maintaining aircraft passenger cabins at comfortable temperatures while, at the same time, eliminating the problems inherent with the use of insulation blankets The successful solution must not be more costly than the current system and, if possible, should be a less expensive system to install, operate and maintain. The present invention fulfills this need in the art.